With the advent of computers, electronic storage can be used to store data sets. Various types of problems can occur that result in losing a dataset. These problems include but are not limited to operator mistakes, disk crashes, site failures and disasters. Mechanisms have been developed for recovering lost datasets. These mechanisms include but are not limited to mirroring a dataset, taking a snapshot of a dataset, and taking backups of datasets. Typically, the more reliable a piece of hardware is the more recoverability capabilities that particular piece of hardware provides and the more expensive it will be. Therefore, multi-tier storage systems have been developed to provide different levels of reliability for different datasets. Some datasets include extremely important data while other datasets include less important data. Datasets with more important data can be stored on a more costly tier that provides a high level of reliability and hence high recoverability and datasets with less important data can be stored on a less costly tier that provides a lower level of reliability and hence lower recoverability. In general, recoverability refers to the ability to recover from data loss or corruption.
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